Orbital defense platforms

[Eternal_Freedom]

THey did manage at least two test firings on Earth for NERVA, but yes, it would have been fired in space. It woudl have replaced the J-2 in the S-IVB, with the S-II slightly modified to get the payload to orbit on it's own (the same way that the S-II for the Skylab launch was modified).

[Sea Skimmer]

More then two as I recall, but they also did them over the hill from the Nevada test site which was already heavily contaminated and no risk existed of a conventional explosion or aerodynamic forces destroying the reactors. Same general area of the Pluto test firing too. None of this makes it a good idea going forward. Otherwise we could claim mustard gas plants in which people catch the leaks in tin cans and dump them down the storm drains are fine... or just shrug at the fact that the Hanford site cleanup had to spend millions of dollars just to deal with contamination spread by fruit flies and radioactive tumbleweeds.

I love nuclear power, but mixing it with flaming explosive piles is just such a bad idea. All the more so when a disaster won't just be a disaster and another strike against nuclear power, but also bring a major space program to a complete halt.

[Eternal_Freedom]

That's why you pair it with the Saturn which had a fantastic service record?

[Sea Skimmer]

The shuttle had just as good a service record for the same number of launches. I wouldn't be so confident that would go on endlessly.

[Eternal_Freedom]

The shuttle had just as good a service record for the same number of launches. I wouldn't be so confident that would go on endlessly.

Very true. Still, NERVA is at least more plausible than ORION, at least in terms of "will they ever be used."

[krakonfive]

Okay so you put a few bombs in orbit. They're orbiting in sight of everyone, just asking for media attantion. And then what?

To attack a ground target you have to deaccelerate them. Yes, you need another rocket just as big as the rocket that took them up to bring them back down.

Two rockets for a single payload? No ty!

[Sea Skimmer]

You most certainly do not need an equal sized rocket to deorbit. A little thing called gravity does that for you. All you have to do is slow down below orbital velocity which takes a tiny fraction of the effort. Notice how say the space shuttle reenters without needing a second set of giant solid rocket boosters and another external fuel tank.

Even if you somehow did have to shed all your velocity, it would still take a much smaller rocket, because you wouldn't be pushing against massive air resistance the way you are when accelerating from a static ground launch.

[ryacko]

Questions:

1. Autoloading recoilless rockets in space, good idea?

2. Launching the equivalanet of a Maus tank into orbit, is this a good idea as well? Although the cramptness might not do wonders for the crew.

[Sky Captain]

NERVA had lousy thrust to weight ratio, it would be unable to lift off from Earth on its own anyway. If you can use it only as third stage then might as well put the thing into stable orbit with chemical rocket and start it there. Then there is no risk a hot nuclear reactor could fall and spread fallout if there is failure.
NERVA would be most useful as an engine for spacecraft that always stay in space.

[Whiskey144]

But the NERVA program did have a competing design, the DUMBO rocket, which *did* have T/W greater than one, and could have been used for liftoff.

But alas, NASA pretty much knew "nope, we're not gonna get to launch nuclear rockets", and so required the program to conform to the existing NERVA engine nozzle, which was incompatible with DUMBO's active cooling needs (and presumably, superior mass flow).

[Sea Skimmer]

NERVA wasn't the last step, Timberwind engines test fired under the later SNTP program had 30:1 thrust to weight ratios and thousand second specific impulse. That should be enough to get into orbit with multiple stages, but then of course you'd be dropping a hot stage back on the planet (unless we build... nuclear fly back booster!). So plans still called for a chemical first stage. The largest Timberwind was also the most powerful nuclear reactor ever built in thermal terms, Timberwind 75 I think it was, but they never actually ran it at full rated power. It would have been over six gigawatts. It ran at 4.2 IIRC.

At the time all SDI funding was suspended in 1992, and with it Timberwind work, it was actually being proposed to fire a prototype from off the coast of Antarctica so if it blew up early in flight it would drop the reactor into the ice. Nuclear power was very attractive to the SDI program because many SDI satellites, as well as some communications satellites that actually did make it into space, required very high orbits. High as in halfway to the moon kind of orbit. That's an expensive thing to do chemically.